Thermostat with frictional snap action



y 1, 1952 R. VALVERDE THERMOSTAT WITH FRICTIONAL SNAP ACTION Filed May 1, 194'!v INVENTOR, v m QM BY ATTORNEY iatented July 1, 1952 THERMO STAT WITH FRIGTIONAL SNAP ACTION Robert Vaiverde, Ne-w'York-N. Y; Application'May 1, 1947, Serial No. 745,163

This invention relates to an improvement in a thermostat with frictional snap action using the principle that tatic friction is greater than moving friction. I have discovered that in applying friction between the moving contact and the fixed contact of a creep type thermostat the'members of the friction couple must, in the direction of motion of the moving contact, be substantially immovable or fixed withrespect to their respective contacts. That is, the friction member attached, directly or indirectly, to the moving contact have no motion with respect to the moving contact in the direction of motion of the moving contact. Likewise, the friction member attached, directly or indirectly,to the fixed contact must have :no motion with respect to the contact .in the directionof motion of the moving contact. The result-is that no motion occurs between the contacts without motion between the friction couple.

In order that there shall he bearing pressure oetween the friction couple, elasticity is provided by one or both members of the couple but not in the direction of motion of the moving contact. lfhere are several forms of friction couples in my invention with the common feature that in the irection of motion of the moving contact both are substantially fixed to their respective con tact-s. One form of my invention uses bimetal for the moving element or thermal motor which I will use to describe myapplication-of static and moving friction. This bimetal normally moves directly in proportion to the change in ambient temperature. In thermal control the. motion is normall microscopic. The separation and joining of contacts is accompanied with dest uctive sparking and any mechanical vibration makes it worse. The contacts weld to cause overheating and they wear out by evaporation to cause loss of'setting.

In my thermostat with increase of temperature the contacts cannot separate until the flexible bimetal has built up a warping force greater than the static force of the frictioncouple. 'Then the contacts separate suddenly and relatively widely.

They continue to separate until the diminishing warping force is exceeded by the force of moving friction, when they would normally come to rest. But if due to the current load aspark occurs. there may be backlash of the moving contact which may cause momentary closure and further destructive sparking. To compensate for the explosive force of the spark, I provide means to ins crease the moving friction force to bring the con tact to rest without backlash.

8 Claims. (Cl. 206*133) friction couple.

Figure =1 shows "a simple form of my friction thermostat with temperatureadjustment.

Figure 2 use detail view of the friction couple used in Figure 1. I

Figure 3 shows a modified form of my thermostat with an L-shaped' bimetal element.

Figure 4A shows another modified form of my thermostat with side friction and using the edgeon ela'sticity'of the bimetal for friction.

Fig. 4B is'an end view of the structure illustrated in Figure 4A, Without the terminals and showina'the friction couple and adjustment.

Fig. 5A is a plan view of a modified construction of the movable contact;

Fig. 5B is an end view of the structure shown inFigJSA.

Fig. 6 shows an application to a crystal oven of two thermostats of the type shown in Fig. '1.

Fig. '7 shows still another modified form of the invention. I

In Figure l on an insulated base i is mounted a'support'z with a 'bimetal strip 3 attached. A contact it carried by the bimetal strip touche a fixed contact 5 whichscrews into a bracket 3 mounted on the base i. Terminals l and Econnect to thermal control circuit of a heater 9 and ci'u'rent terminal lil. Fixed into the'base l is a friction wire H which presses against the tip i2 atthe free end of the bimetal to form a The friction wire H is at an acute-angle to the bimetal strip 3 so that moving friction pressure increases and compensates for the explosive force of sparking as the contacts a and 5 open. This friction couple is shown in I. Figure'z in solid lines for the contacts-closed position of friction wire H and-friction tip I2.

and in dotted lines after the contacts d and 5 open. The elastic wire l [is pushed into'its dotted line position to increase the frictional pressure asthe bimetal 3 moves into its dotted line position. This andsimilar friction couples produce a true snapaction without backlash. On closure the static friction. again builds up potential energy in the bimetal until snap action motion occurs with a diminishing moving friction to opposea possible explosive spark and for a firm contacting.

Fig; 3 shows another way'of causing the friction pressure to increase as the contacts open. The L.-shaped bimetal element l3 has two function's; the horizontal part opens the contacts H The friction plate I! is an insulator and fixed to an arm l9 which is fixed to the contact I5. Again this friction couple is unyielding in the direction of motion of the moving contact I4 so that no motion occurs between the friction couple unless the contacts separate. A pressure adjustment for the friction couple is made with a screw that threads through the arm l9 and into contact with a bracket 23 of the thermostat assembly. By joining the bimetal element supporting bracket 22 to the contact bracket 23 with insulating cement 24 the thermostat is fixed to only one terminal 25 and the circuit is completed to a second terminal 26 by a pigtail 21.

Another friction couple, Figs. 4a and 4b, is obtained by the edge-on pressure of a bimetal element 30 against an adjustable finger 3|, a part of a bracket 32. The free end of the bimetal 30 is formed into a shoe 29 which presses against insulation enamel 28 on the finger 3|. This finger 3| is adjusted to slope outward so that the edge-on friction pressure increases as the contacts 33 and 34 open. Again there is no friction couple motion in the direction of motion of the moving contact unless the contacts separate or close.

I have discovered that the current capacity of my thermostat is increased by thermally and electrically insulating the moving contact from its bimetal. In Figs. 5a and 51) there is shown a contact of bimetal assembly which produces an extended path through the contact to permit contacting-heat to dissipate. A silver strap contact 35 is attached to a bimetalstrip 35 with a thermal and electric insulating cement 3'! and K the contact and bimetal are joined electrically with a connector 38 at the greatest distance from the contact point. The connector 38 may extend directly to the contact terminal without touching the bimetal. In the crystal oven application shown in Fig. 6, a bimetal strip 39 is mounted in a narrow section of square plastic tubing 40 with its contact 4| touching an adjustable contact 42 which is connected to a terminal 43. This bimetal thermostat connects at terminal 44 to a heater coil 45 molded into the plastic tubing 40. A friction spring 46, pressure adjusted by a screw 41, makes a friction couple with the bimetal tip 48 in the same manner as in Fig. 1. metal strip 50, contacts 5| and 52, and terminal 53 form a thermostat to control another heater wire 54 molded into plastic tubing 40; A front and back panel, not shown, make an oven of the plastic tubing 40 which holds an electronic crystal 55 with terminals 55 and 51. In operation the bimetal strip 39 controls a booster heater and the bimetal strip '53 controls the heater 54 to keep the crystal at a constant temperature. In Fig. 7 a bimetal strip with upper and lower portions 58 and'59, and with an adjustable contact 60 and an insulated contact 6|, is mounted on a terminal post 62. One part of the friction couple is a leaf spring 63 attached to the end of the lower portion of the bimetal strip 59 with its polished surface in contact with an enamel tipped end 64 of an adjustable friction screw 65, the other part of the friction couple.

The contact screw 68 and the friction screw 65 are mounted without play in a looped end 66 of the upper portion of the bimetal strip 58. Any motion between the upper and lower portions 58 and 59 of the bimetal strip under the influence of heat causes. an equal motion be- Similarly a terminal 49, bi-

tween the two parts 63 and 64 of the friction couple and an equal motion between the two parts 60 and (ii of the electrical contact. This motion in either direction is a snap action. A pigtail 61 connects insulated contact BI and a terminal 68 to complete the circuit.

The preferred embodiments of the invention have been illustrated and described but changes and modifications can be made and some features of the invention can be used in different combinations Without departing from the invention as defined in the claims.

I claim as my invention:

1. A thermostat including contacts, one of which is movable with respect to the other, a thermal motor connected with the movable contact, two friction elements, including a first element which is connected with the movable contact and fixed with respect to the movable contact in at least the direction of movement of said movable contact, and a second element which is relatively fixed in the direction of movement of the movable contact, a friction surface on one of said elements and with which the other friction element contacts, said friction surface of one element extending at an acute angle to the direction of movement of an adjacent portion of the other element so as to change the pressure between the surfaces progressively as one friction surface moves along the other.

2. A thermostat comprising two bimetal strips supported at corresponding ends and disposed so as to warp in opposite directions with change in temperature, contacts carried by the respective strips in position to move toward and from one another as the strips warp, and friction elements carried by the strips and resisting movement of the strips with change of temperature, each of said friction elements being immovable, with respect to the strip that carries it, in at least the direction of movement of the strip that carries it.

3. A thermostat comprising a substantially V- shaped bimetal thermal motor, a fixed support for the thermal motor, a contact carried by one leg of the V-shaped bimetal, electrical insulation between said contact and the bimetal, a contact carried by the other leg of the V-shaped bimetal and adjustable toward and from the insulated contact to change the temperature at which the contacts come together and at which they separate, a friction element comprising a strip attached to one of the legs of the V-shape bimetal and extending across and beyond the other leg of said bimetal, and an adjustable screw on said other leg in position to slide along the friction element as the contacts move toward and from one another.

4. A creep type thermostat, as described in claim 1, and in which one of the friction elements is connected with the thermal motor and is defiectable with respect to the other friction element but non-defiectable with respect to the thermal motor in the direction in which the thermal motor moves the friction element.

5. A creep type thermostat, as described in claim 1, and in which the fixedcontact is attached to a switch frame and the movable contact is fixed to the thermal motor, the frame being electrically insulated from the motor and one of the friction elements being fixed to the portion of the thermal motor that is connected with the movable contact and being resiliently pressed against an electrically insulated part of the frame but non-deflectable with respect to the moving contact in the direction of motion of the movin contact. a

6. A thermostat as described in claim 1, and in which the thermal motor comprises a part of bimetal strip having a portion which is relatively fixed and a portion which is movable, one contact comprising an element that extends around at least a part of both upper and lower surfaces of the movable portion of the bimetal strip, a layer of electrical and thermal insulating material between the bimetal and the contact element that extends around the bimetal, the other contact being fixed in position to be touched by a surface of said contact element on one side of the bimetal strip when the bimetal warps in one direction, and a flexible conductor connected with a portion of the contact element on the other side of the bimetal for establishing a circuit to a terminal of the thermostat.

7. A thermostat. including contacts, one of which is movable with respect to the other, a thermal motor connected with the movable contact, two friction elements including a first element which is connected with the movable contact and movable therewith, a second element which is connected with the other contact, a friction surface on one or said elements and with which the other friction element contacts, one of the friction elements having a resilient structure that holds said friction elements in contact with one another, the entire length or said resilient structure extending at an acute angle to the direction of movement of an adjacent portion of said other friction element.

8. A thermostat as described in claim 1 and in which the first friction element has a fixed end and a movable end, and said first friction element is shaped to provide resilience for shifting the free end, across as well as along the path along which the free end of said first element is urged by the thermal motor, and the friction surface is on a member opposing movement of the free end of said first element and against which said free end is held by the resilience of said first element.

ROBERT VALVERDE.

REFERENCES CITED The following references are of record in the 

